一、查詢不顯示全部列——select的使用

第一種情況——直接選定要顯示的列

//    SELECT id,name FROM user WHERE (name LIKE ? AND age < ?)
    @Test
    public void selectByWrapperSupper(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.select("id","name").like("name","J").lt("age",20);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第二種情況——反向設(shè)定不要顯示的列（適用于要顯示的列有很多的情況）

//    SELECT id,email FROM user WHERE (name LIKE ? AND age < ?) 
    @Test
    public void selectByWrapperSupper2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        queryWrapper.like("name","J").lt("age",20).select(User.class,
                info->!info.getColumn().equals("age")&&!info.getColumn().equals("name"));

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

二、方法的第三個參數(shù)——condition執(zhí)行條件的使用

//    SELECT id,name,age,email FROM user WHERE (name LIKE ?) 
    @Test
    public void testCondition(){
        String name = "J";
        String email = "";
        condition(name, email);
    }
    private void condition(String name,String email){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

//        if(StringUtils.isNotBlank(name)){
//            queryWrapper.like("name", name);
//        }
//        if(StringUtils.isNotBlank(email)){
//            queryWrapper.like("email", email);
//        }

//        使用第三個參數(shù)condition參數(shù)來控制條件后
        queryWrapper.like(StringUtils.isNotBlank(name),"name",name)
                .like(StringUtils.isNotBlank(email), "email", email);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

三、當(dāng)使用實體作為條件構(gòu)造器的構(gòu)造參數(shù)時

注1：實體作為構(gòu)造參數(shù)和條件構(gòu)造器單獨(dú)設(shè)置的條件同時存在，所以注意不要設(shè)置重復(fù)了。

//    SELECT id,name,age,email FROM user WHERE name=? AND age=? AND (name LIKE ? AND age < ?)
    @Test
    public void selectByWrapperEntity(){
        User user = new User();
        user.setName("Jack");
        user.setAge(20);

        QueryWrapper<User> queryWrapper = new QueryWrapper<>(user);

        queryWrapper.like("name","J").lt("age",20);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

注2：實體作為構(gòu)造參數(shù)傳入后如果想做模糊查詢，只需要在實體上對應(yīng)字段添加注解

    @TableField(condition = SqlCondition.LIKE)
    private String name;

注3：%s表示字段，#{%s}表示字段對應(yīng)的值，自定義一個條件

//    SELECT id,name,age,email FROM user WHERE name LIKE CONCAT('%',?,'%') AND age<? AND (name LIKE ? AND age < ?) 
    @TableField(condition = "%s&lt;#{%s}")
    private int age;

四、allEq用法

第一種情況：某個條件的值為null時，查出來的sql就是is null

//  SELECT id,name,age,email FROM user WHERE (name = ? AND age IS NULL) 
    @Test
    public void selectByWrapperAllEq(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq(params);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第二種情況：某個條件的值為null，allEq方法添加第二個參數(shù)為false時，查出來的sql忽略值為null的條件

//  SELECT id,name,age,email FROM user WHERE (name = ?) 
    @Test
    public void selectByWrapperAllEq(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq(params,false);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第三種情況：allEq方法中添加過濾條件參數(shù)，只保留符合條件的參數(shù)作為條件

//  SELECT id,name,age,email FROM user WHERE (age IS NULL)   
    @Test
    public void selectByWrapperAllEq2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq((k,v)->!k.equals("name"),params);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第四種情況：在上面第三種情況基礎(chǔ)上再添加第三個布爾條件為false，忽略值為null的條件

//  SELECT id,name,age,email FROM user 
    @Test
    public void selectByWrapperAllEq2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq((k,v)->!k.equals("name"),params,false);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }

第五種情況：在上面基礎(chǔ)上添加condition執(zhí)行條件

//  SELECT id,name,age,email FROM user WHERE (name = ?)   
    @Test
    public void selectByWrapperAllEq2(){
        QueryWrapper<User> queryWrapper = new QueryWrapper<>();

        Map<String,Object> params = new HashMap<>();
        params.put("name","Jack");
        params.put("age",null);
        queryWrapper.allEq(StringUtils.isNotBlank((String)params.get("name")),(k,v)->!k.equals("age"),params,false);

        List<User> userList = userMapper.selectList(queryWrapper);
        userList.forEach(System.out::println);
    }